The present invention relates to a power transmission device, an electronic instrument, a waveform monitoring circuit, and the like.
In recent years, non-contact power transmission (contactless power transmission) that utilizes electromagnetic induction to enable power transmission without metal-to-metal contact has attracted attention. As application examples of non-contact power transmission, charging a portable telephone, charging a household appliance (e.g., telephone handset), and the like have been proposed.
As related-art non-contact power transmission technology, a power transmission device has been known which implements data transmission from a power reception device (secondary side) to a power transmission device (primary side) by means of load modulation (e.g., JP-A-2006-60909). The power transmission device detects a change in power-reception-side (secondary-side) load state due to foreign object insertion or data transmission by detecting the induced voltage in a primary coil using a comparator or the like.
The above-mentioned power transmission device generates an induced voltage signal input to a power transmission control device by means of voltage division using a resistor. Therefore, the waveform is reduced due to voltage division, whereby the load state detection accuracy cannot be improved to a satisfactory level.